A system that effectively measures a catheter's performance in vitro is useful in designing catheters for implantation in patients. Because various physiological factors (e.g., blood flow, blood pressure, vessel dimensions, etc.) impact the operation of a given catheter, to effectively compare the performance of catheters with different design parameters, one would need a simulation system that provides user control of the physiological parameters. It may also be beneficial to have a simulation system that would allow the design engineers to set a baseline to measure and compare the performance of different catheter designs.
Thus, an in vitro system that provides design engineers a controlled environment to test various design parameters and optimize the performance of catheters is desirable. In particular, a system that properly simulates the flow and pressure characteristics in a human heart is useful for testing dialysis catheters. One of the key parameters that govern the performance of a dialysis catheter is the recirculation rate. The measurement of the recirculation of blood is an important variable with respect to dialysis catheters because it is advantageous to know the amount of cleaned blood that is entering back into the catheter and mixing with the “dirty” blood. The ability to test and effectively predict the recirculation rate of the catheter in a simulated implant condition allows the engineers to design a catheter that would minimize recirculation and improve the efficiency of the catheter. However, since the recirculation rate in vivo is affected by various physiological factors, a system that can provide effective recirculation rate measurements needs to properly simulate the various physiological factors (e.g., blood flow rate, blood pressure, dimensions of the vessel, etc.).
Over the years, various systems have been designed for measuring recirculation of blood in dialysis catheters. Examples of some of these designs are disclosed in U.S. Pat. No. 5,588,959, titled “HEMODIALYSIS RECIRCULATION MEASURING METHOD” issued to Ahmad et al., dated Dec. 31, 1996; U.S. Pat. No. 5,644,240, titled “DIFFERENTIAL CONDUCTIVITY HEMODYNAMIC MONITOR” issued to Brugger, dated Jul. 1, 1997; U.S. Pat. No. 5,685,989, titled “METHOD AND APPARATUS TO MEASURE BLOOD FLOW AND RECIRCULATION IN HEMODIALYSIS SHUNTS” issued to Krivitski et al., dated Nov. 11, 1997; U.S. Pat. No. 6,167,765 B1, titled “SYSTEM AND METHOD FOR DETERMING THE FLOW RATE OF BLOOD IN A VESSEL USING DOPLLER FREQUENCY SIGNALS” issued to Weitzel, dated Jan. 2, 2001; U.S. Pat. No. 6,189,388 B1, titled “ACCESS FLOW MONITORING USING REVERSAL OF NORMAL BLOOD FLOW” issued to Cole et al., dated Feb. 20, 2001; each of which is incorporated herein by reference in its entirety.
Many of the existing systems do not effectively simulate the blood flow (e.g., vortex flow due to heart chamber shape and vessel wall characteristics, etc.) and blood pressure (blood pressure change due to the cycling of the heartbeat, etc.) changes surrounding the catheter in an implanted condition. Since the amount of recirculation is affected by the turbulence and various fluid dynamics at the distal end of a dialysis catheter due to the vessel and the heart's physiological characteristics, a simulation system that can simulate these characteristics and variables may be more effective in measuring the actual recirculation rate in an implanted environment. Thus, it may be desirable to provide a realistic cardiovascular simulation environment for the testing of dialysis catheters. It may also be beneficial to allow the operator to control the fluid flow, pressure dynamics, and physical characteristics of the simulation system, and preset these parameters to conditions that simulate the environmental condition in which the catheter would be utilized in an actual human body.